Manufacture of microbiologically resistant alkylaryl sulfonates from sulfonate mixtures by microbiological oxidation



United States Patent MANUFACTURE OF MICROBIDLQGICALLY RE- SISTANT ALKYLARYL SULFONATES FROM SULFGNATE MIXTURES BY MICROBIOLOGI- CAL OXIDATION Raymond C. Allred and Robert L. Huddleston, Ponca City, Okla, assignors to Continental Gil Company, Ponca City, Okla, a corporation of Delaware No Drawing. Filed July 9, 1962, Ser. No. 208,557

7 Claims. (Cl. 195-99) This invention is related to the manufacture of alkyl arylsulfonate surface active agents. More specifically, this invention is directed to manufacture of microbiologically resistant alkylarylsulfonates for industrial use.

The alkylarylsulfonates are compositions formed by alkylation of an aromatic hydrocarbon, followed by sulfonation, and finally neutralization with a basic substance. A typical example is sodium dodecylbenzenesulfonate,

12 25 S OaNa in which the C H substituents of individual products possess a variety of configurations and which has proved to be the most useful as a detergent of any of the group. When the aliphatic hydrocarbon substituent group is lengthened greatly, or at least is made much larger, the product becomes less effective as a detergent in water, because of its lesser solubility. The same elfect is apparent if the aromatic nucleus is made larger, as when naphthalene is substituted for benzene. By decreasing the size of the alkyl group, water solubility is increased, detergency is decreased, and wetting power is increased. By decreasing the size of the alkyl group and at the same time increasing the size of the aromatic nucleus, decrease in detergency may be avoided so that the resulting products are powerful wetting agents but still possess considerable detergent ability. Examples of this type of product are sodium diisopropylnaphthalenesulfonate and sodium diisobutylnaphthalenesulfonate, which are useful industrially as degreasing detergents and emulsifiers. These latter products are not suitable for household use because they have a tendency to remove the oils from the skin, causing a dermatitis. Multiple alkyl substituent groups on the aromatic nucleus, especially if the substituents are small in size, accentuates the wetting and penetrating ability of alkylarylsulfonates in aqueous systerns. The wetting and penetrating ability of products such as sodium xylenesulfonate, for example, is so great that such products are hydrotropic solutizers for various organic substances which normally possess only very limited solubility in water.

Because the surface active properties of the alkylarylsulfonates may be modified readily to suit various applications, as discussed above, and because they are produced readily from inexpensive raw materials, they find many important applications in industry. Sodium dodecylbenzenesulfonate, in combination with minor amounts of higher and lower benzenesulfonates has become accepted as the most useful synthetic detergent for household use. It is true that the detergency of this prodnot is not outstanding, when compared to ordinary soaps, for such applications as soft water washing of cotton goods and shampooing of hair. However, when combined with suitable builders, water softeners, peptizers and other auxiliary agents, this product now gives acceptable performance under a much greater variety of household situations than has ever been possible with soap, and at a reasonable price. Alkylbenzenesulfonate detergents of this type now are used for home laundering, dishwashing and other purposes in tremendous quantities. Certain mass production economies have served to reduce the cost of these products to the point at which other products are no longer competitive, with the result that industry, too, depends upon the use of surface active agents of this, or a very similar type, which can be manufactured in the same production facilities.

The widespread household use of alkylarylsulfonate detergents has produced some unexpected and rather serious problems in sewage disposal plants, water treating plants and in the normal use of natural ground waters and surface waters. Unlike the soaps which they have to a great extent replaced, the alkylarylsulfonates are not adequately decomposed by the microbiological floras of sewage treatment plants, surface waters and ground waters. Thus they are able to pass through waste treating systems and into rivers and streams while still retaining their original properties. Some of the problems encountered by the presence of undecomposed sulfonates are:

(1) Excessive foaming in sewage treating plants which has resulted in health hazards and reduced operating efiiciency of the plants.

(2) Possible toxic effects to aquatic life in streams and rivers.

(3) Production of taste, odor and foam in drinking water.

(4) Interference with flocculation and precipitation in water treating plants.

In response to an undeniably serious situation, research is being carried out both with the purpose of increasing the effectiveness of sewage and water treatment systems and to develope processes for manufacture of detergents which are referred to variously as disposable, microbiologically decomposable, biologically soft, biodegradable or biologically degradable. By these expressions is meant that the detergent can be consumed by the bacteria in the sewage disposal plant within a reasonble length of time. If a long period is required for complete degradation to non-surface active or non-foaming substances, the detergent will be carried into streams with the effluent from the disposal plant and will be a source of pollution. Thus, the limits of disposability are not the same as the absolute limits of susceptibility to microbiological attack. It seems likely that no alkylarylsulfonate is completely immune to microbiological attack, although it is certainly true that a few specific compounds of this type have resisted attack for a period of several months. As a practical matter, since the residence time of sewage in the average fermentation treatment process is within the range of from about 2 to 12 hours, a completely microbiologically disposable detergent should become fully degraded Within about 5 or 6 hours. There are now on the market a few new detergent compositions which are claimed to be greatly improved in this respect. One is said to be as much as 94% disposable, compared 3 with about 68% for the best of the regular commerical alkylbenzenesulfonates. Processes have been proposed for manufacture of alkylbenzenesulfonates, said to be completely disposable by virtue of the fact that the alkyl substituent groups are completely straight chains.

It should be fairly obvious that straight chain alkyl substituents are highly susceptible to microbiological attack, since they are identical to the hydrocarbon portions of soap molecules. However, commercial detergents which are better than 50% disposable may contain no completely straight chain alkyl substituents whatever. It is apparent that a rather broad class of alkyl substituents must be disposable, or at least there must exist a definite class of alkyl substituents which are resistant to microbiological attack, so that sulfonates containing these substituents are not disposable. We have discovered that salts of a group of alkylarylsulfonic acids of the type are microbiologically resistant when X, Y and Z are selected from the group consisting of hydrogen and hydrogen substituent groups containing no more than 4 consecutive methylene carbon atoms arranged in any terminal straight chain portion thereof, the total number of carbon atoms in Groups X, Y and Z being from 5 to 17 inclusive. This class of compounds includes the portion of household alkylbenzenesulfonate detergents which is considered to be biologically resistant.

In many industrial applications, aqueous systems containing surface active agents are used repeatedly for long periods of time. This is true of cutting and grinding fluids of the oil-in-water dispersion type of degreasing baths and various washing solutions. In direct contrast to household use requirements, in industrial applications the presence of detergents which are easily susceptible to microbiological attack becomes a definite nuisance and often a health hazard as well. It is precisely the class of resistant alkylarylsulfonates defined above which is particularly desirable for industrial purposes and it is the primary object of this invention to provide a method of manufacturing mixtures of compounds of the defined type, substantially free of non-microbiologically resistant alkylarylsulfonates.

It is a further object of this invention to provide a method for manufacturing mixtures of compounds of the defined type which utilizes microbiological oxidation as one of the process steps. Other objects and advantages may become apparent on reading the following detailed description and specific examples.

Briefly, our invention may be defined as a method of manufacture of a mixture of water-soluble salts of sulfonic acids of the type in which X, Y and Z are selected from the group consisting of hydrogen and hydrocarbon substituent groups containing no more than 4 consecutive methylene carbon atoms arranged in any terminal straight chain portion thereof, the total number of carbon atoms in said groups X, Y, and Z being from 5 to 17 inclusive, employing the following steps:

(a) Oxidizing microbiologically a mixture of salts of alkylarylsulfonic acids having branched alkyl groups containing from 6 to 18 carbon atoms derived from polymers of propene to yield a product mixture;

4 (b) Recovering water-soluble salts of alkylarylsulfonic acids from the product mixture of step (a).

Since it is essential to the success of the process that suitable alkylarylsulfonate starting material be employed in the microbiological oxidation step, this subject will be discussed first.

(I) EVALUATION AND SELECTION OF ALKYL- ARYLSULFONATES AS RAW MATERIALS The suitability of an alkylarylsulfonate for use in the present process may be judged with the aid of laboratory test techniques which are presented below.

(A) Microbiological Methods The following representative bacteria cultures have been used in evaluating the proportion microbiologically resistant material in alkylarylsulfonate mixtures:

(l) A mixed culture, referred to herein as the laboratory culture, which was originally a pure culture of Escherichia coli. This culture was proven stable in its ability to decompose sulfonate detergents and its rate of decomposition of alkylarylsulfonates was found to be equivalent to other cultures obtained from soil, activated sludge sewage plants and untreated river water.

(2) A culture obtained from an untreated sample of river water and which was only slightly acclimated to an environment containing alkylarylsulfonates by two consecutive passes in a medium containing sodium n-dodecylbenzenesulfonate. This culture is referred to herein as the river water culture.

(3) A culture obtained from a sample of activated sludge from a municipal sewage treatment plant.

The biodegradability of various alkylbenzenesulfonates has been evaluated according to the following procedure:

A fermentation medium was made up according to the following recipe:

Ammonium chloride g 4.0 Dipotassium phosphate g..- 1.0 Magnesium sulfate g 0.25 Potassium chloride g 0.25 Ferric sulfate Trace Yeast extract g 0.3 Deionized water ml 1,000 Substrate (sulfonate) mg 30 This medium was added in l-liter amounts to 2-liter Erlenmeyer flasks and sterilized by autoclaving 15 minutes at 20 pounds steam pressure.

After cooling to room temperature, the flasks were inoculated with 10 ml. of a 48 to 72-hour old culture. The flasks were then placed on a gyratory shaker and allowed to shake for 30 minutes. At this time, 10-ml. aliquots in triplicate were removed from each flask and transferred to SO-ml. flasks. These samples served as methyl green controls, indicating starting sulfonate concentrations in each flask. The 10-ml. samples were made acid by adding 2 ml. of concentrated HCl. This ceased microbial activity in the samples. The shaker flasks were replaced on the shaker and allowed to shake for 7 days. At predetermined time intervals 10 ml. samples were removed from the flasks for surface tension measurement and colorimetric analyses.

After the weeks incubation on the shaker, the flasks were made acid with ml. of concentrated HCl to stop further biological degradation. Triplicate 10ml. aliquots were then again removed by colorimetric analysis. The remainder of the flask contents were used for vapor chromatographic analysis.

The two analytical methods used to evaluate the results of bacterial action can be described as follows: (1) An assay method which indicates the percentage of unaltered sulfonate remaining in the sample (this procedure is a colorimetric test utilizing methyl green dye) and (2) desulfonation-vapor chromatrographic method which indicates qualitatively the amount of original alkylate remaining, structural changes of the original substrate, selective attack of isomeric forms, and appearance of intermediate oxidation products. These two analytical techniques are described in brief detail below.

(B) Analytical Methods (1) METHYL GREEN COLORIMETRIC ANALYSIS This is a colorimetric procedure involving the formation of a complex between basic methyl green dye and an anionic detergent in Water solution. The complex, being organic soluble, is removed from the aqueous reaction medium by extraction with benzene. Excess dye, being Water soluble, remains in the water phase and does not interfere.

The optical density of the extracted complex is then read in a spectrometer and compared with a standard. Since only 0.03 mg. of detergent is required for this analysis, the remainder of the sample can be used for desulfonation-vapor chromatrographic analysis. For highest accuracy, it has been our practice to analyze all samples in triplicate.

2 DESULFONA'IION-GAS-LIQUID PARTITION CHROMATOGRAPHY The biodegraded samples consist of about 1 liter of the aqueous medium made acid with 80 ml. of concentrated HCl. In order to decompose the bacterial cells and free contained or absorbed sulfonate, the medium is hydrolyzed by boiling for 20 minutes. The solution is then neutralized with NaOH and the solution passed dropwise (50-70 drops per minute) through a column containing gm. of charcoal (Nuchar C490). The absorption of the sulfonate and sulfonate intermediates on the carbon is quantitative as indicated by labeled carbon studies. Desorption from the carbon is also quantitative as also shown by tagged carbon. The desorption is accomplished by elution with 5050 benzene-methanol- 1 percent NH OH solution. After evaporation of the solvent, the residue is taken up and desulfonated in phosphoric acid. The steam distilled material is collected in a water trap and recovered by pentane extraction. The pentane extractions are combined in a test tube, and the pentane is removed by careful application of low vacuum at room temperature. The residue is then examined by G.L.P.C. techniques.

(3) SURFACE TENSION In addition to the above techniques, surface tension measurements made at intervals provide some indication of the progress of microbiological oxidation. Qualitative indications of the extent of microbiological degradation of the sulfonate were obtained by using a Du Noiiy tensiometer. Aliquots of 10 ml. were. removed from shake flask cultures at timed intervals and surface tension was determined. Inoculated flasks containing no surface active agents served as controls. This technique of analysis was found to be useful only when the sulfonate at a concentration of 30 mg. per liter possessed the ability to reduce the surface tension of the medium to 55 dynes/ cm. or lower.

(C) Results of Testing Difierent Types of Alkylarylsulfonates Several alkylbenzenesulfonates having different types of alkyl substituent groups were subjected to biodegradation according to the procedure outlined above, using both the river Water bacterial culture and the laboratory culture, the yield of microbiologically resistant sulfonate being determined by means of the methyl green colorimetric test. Results are summarized in the table below.

(5) By alkylation with chlorinated straight-chain parafilnic hydrocarbon 0 0 (6) Commercial kerylbenzene-sulfonate 38 (7) By alkylation with mixture of straight-chain efins- 0 0 E8) l-Butyl-l-methylamyl-. 9) 1-Butyl-1-propy1hexy1- 95 (10) l-Butyl-l-methyloctyl 0 (11) By alkylation With olefin obt ned by erac ing paraffin wax 0 (12) 1-Propy1amyl- 50 (13) l-Propylheptyl- 0 (14) 1-Butyl-l-methylhcptyl- 50 (15) 1-Butyl-1-propylhexyl- (16) By alkylation with mixture of branched olefins averaging 13 carbon atoms made by polymerization of propene over supported phosphoric acid catalyst 93 100 (17) By alkylation With mixture of branched olefins averaging 15 carbon atoms made by polymerization of propene over supported phosphoric acid catalyst 86 100 The effect of the number of consecutive methylene groups in straight chain segments of alkyl substituents is demonstrated in the tabulated results of tests made on pure alkylarylsulfonates. In the case of l-propylamylbenzenesulfonate, it will be noticed that although the straight chain is short, the fact that the alkyl substituent is secondary rather than tertiary detracts from its resistance. Tertiary alkyl substituents are preferred.

From examination of the data in this table it may also be seen that use of the laboratory culture which was already acclimated to an alkylarylsulfonate environment provided a rather severe test of microbiological resistance. In industrial applications, one can expect a surface active agent to give consistently satisfactory performance, only if it is able to pass a severe test.

The product containing alkyl groups derived from highly branched olefin obtained by condensation of propene dimer in the presence of phosphoric acid is especially interesting, since it shows consistently high resistance to microbiological degradation. In the strictest interpretation of the terminology, this highly branched olefin must be considered a polymer of propene, but is obtained in a specific manner. We have found that when the branched olefin is made by further consideration of propene dimers and trimers, the content of microbiologically resistant alkylarylsulfonate in the product is, in general, considerably higher than occurs in the case of branched olefin made by (1) continuous propene polymerization or (2) condensation of dimer or trimer with additional propene until the desired molecular Weight is achieved. A reasonable explanation of this phenomenon is that in the condensation of dimer and trimer, a small number of different structures is possible, and all of these are highly branched, whereas addition of propene can result in formation of straight chain terminal structures of more than 5 carbon atoms within the olefin molecules.

By way of illustration, there was subjected to microbiological oxidation according to the general procedure described above, a commercial alkylbenzenesulfonate product. The alkyl groups of this product contained an average of 12 carbon atoms and were derived from branched olefin made by polymerization of propene in the presence of a solid phosphoric acid catalyst, with some recycling of propene dimer and trimer to the reaction zone. Periodic colorimetric analyses were made by the methyl green technique described above, so as to obtain an indication of the progress of microbiological degradation. The period of the test was in this instance extended to eight weeks. Pure cultures, activated sludge culture, the river water culture and the laboratory culture were all used for testing. The data presented below may be regarded as typical.

Thus, it appears that for manufacture of a highly resistant surface active agent from such a sulfonate mixture, approximately forty percent of the material must be removed by the microbiological oxidation step of the present process, and about twenty percent must be removed to yield what might be regarded as commercially acceptable material.

When as much as twenty percent of the untreated alkylarylsulfonate must be consumed in the microbioligical oxidation step, the volumes of aqueous solution to be handled and the residence time in the reactor become so great as to present formidable problems. In general, it is economically feasible to convert to oxidized substances a maximum of about 10 percent of the alkylarylsulfonates by this step, and it is preferred to consume less than about percent. When yield is thus maintained above about 95 percent, it is feasible to operate with fairly concentrated solutions and short residence times and recover the product by filtration, followed by spray drying. Water-insoluble by-products are removed, for example, by passing through a clarifying filter containing a bed of finely-divided solid filter medium, and volatile, soluble byproducts are removed in the spray-drying step. Soluble inorganic by-products, in general, do not detract from the acceptability of the product, so that removal is unnecessary. If it is desired to remove inorganic salts, there are known methods of desalting which may be employed. The process steps are discussed in detail below.

(II) MICROBIOLOGICAL OXIDATION AND PRODUCT RECOVERY The potential advantages of continuous industrial fermentation processes, as compared with batch processes are discussed in various publications and are well known. Continuous operation is preferred in the present process so as to maintain a high rate of production and to separate the cell growth phase of the fermentation from the digestion phase. This separation of phases permits use of more concentrated solutions and reduction of residence time in the digestion phase. Below are described briefly several types of continuous fermentations which are applicable to the present process.

(A) Single Stage In single stage fermentations the entire operation is completed under steady-state conditions in one vessel, the nutrients being added and the living cells and chemical products being removed simultaneously at the same continuous rate. Processes of this type are particularly suitable, for example, in yeast fermentation, in which the yeast itself is a major product. The present method may be operated in this manner, especially if the bacteria culture is recovered for use in producing a feed supplement or fertilizer.

(B) Semi-Continuous Fermentations of the semi-continuous type are single or multiple stage operations in which the feeding and withdrawing are accomplished intermittently rather than 8 continuously. For example, when a fermentation batch has reached its maximum yield and fermentation has therefore begun to decline, a part of the fermentor contents may be harvested and the fermentor recharged with fresh medium, and possibly also freshly grown bacterial cells, as in the present process, so that another cycle may begin. Since alkylarylsulfonates are mostly produced in bath processes, semi-continnuous operation of the fermentation step of the present method is especially convenient.

(C) Modified Single-Stage Modified single-stage continuous fermentations employ fermentation apparatus designed to permit the re-use of bacterial cells, either by effecting separation of the cells from the chemical product and return to the reactor, or by retaining the cells in the reactor during removal of the chemical product. This type of continuous operation is particularly applicable to fermentations in which it is primarily the chemical product which is desired, rather than the bacterial cells, as for example, in the process of this invention. (D) Multiple-Stage In this type of fermentation a battery of two or more fermentors are operated in series, fresh medium being fed into the first, the eflluent from it passed to the second, and so on through the series. This type of procedure, carried out on a semicontinuous basis, is the preferred method of conducting the fermentation step in the present invention, since cell growth may be emphasized in the first fermentor where the concentration of nutrients is higher, and in the final stage the emphasis may be put on removing the last traces of biodegradable alkylarylsulfonate from the product.

It is preferred to control the first stage of the multiple stage fermentation internally, by controlling nutrient level, and to some extent also externally, by controlling bacterial population. The low nutrient level in the final stage provides sufficient internal control, the bacteria in this stage being fed at which might be termed a subsistence level. Bacteria which are removed from the product by filtration may be pasteurized and dried and employed as high-protein animal feed supplements.

The preferred type of fermentor is a ventilated vessel in which the contents are subjected to intense aeration. The effluent from the final fermentation stage is preferably passed through a defoamer and the separated foam subjected to a foam-breaking technique, followed by recycle to the fermentation step. The defoamed efiiuent is then filtered to remove bacterial cells and is treated by spray drying or steam distillation to yield either a dry powder or an aqueous liquid concentrate product.

The alkylarylsulfonate products obtained by this method are particularly useful industrially in applications in which solutions containing them are kept in use for long periods of time, or are frequently clarified and re-used. Since these products contain a minimum of nutrients for bacteria, it is feasible to control bacterial action in solutions containing them by use of bactericides at very low levels of concentration. This characteristic is very advantageous in applications in which the toxic and irritant properties of surface active solutions must be kept as low as possible.

The invention having thus been fully and clearly described, what is desired to be secured by Letters Patent is defined in the appended claims. It is understood, of course, that equivalents known to those skilled in the art are to be construed as within the scope and purview of the claims.

We claim:

1. A method of manufacture of a mixture of watersoluble salts of sulfonic acids of the type Aryl in which X, Y, and Z are selected from the group consisting of hydrogen and hydrocarbon substituent groups containing no more than 4 consecutive methylene carbon atoms arranged in any terminal straight chain portion thereof, the total number of carbon atoms in said groups X, Y, and Z being from 5 to 17, inclusive, said method comprising the steps:

(a) oxidizing microbiologically a nutrient medium containing a mixture of salts of alkylarylsulfonic acids employing bacteria selected from the class consisting of a mixed culture containing Escherichia coli, a culture obtained from untreated river water, and a culture obtained from sewage treatment plant activated sludge, said alkylaryl sulfonic acids having branched alkyl groups in Which the total number of carbon atoms varies within the range of 6 to 18, said alkyl groups being derived from polymers of propene to yield a product mixture, and

(b) recovering water soluble salts of alkylarylsulfonic acids from the product mixture of step (a).

2. A method according to claim 1 in which the water soluble salts of alkylarylsulfonic acids are recovered in step (b) in the form of a dry powder.

3. A method according to claim 1 in which the watersoluble salts of alkylarylsulfonic acids are recovered in step (b) in the form of an aqueous liquid concentrate.

4. A method of manufacture of a mixture of watersoluble salts of sulfonic acids of the type in which X, Y, and Z are selected from the group consisting of hydrogen and hydrocarbon substituent groups containing no more than 4 consecutive methylene carbon atoms arranged in any terminal straight chain portion thereof, the total number of carbon atoms in said groups X, Y, and Z being from 5 to 17, inclusive, said method comprising the steps:

(a) oxidizing microbiologically a nutrient medium containing a mixture of salts of alkylarylsulfonic acids employing bacteria selected from the class consisting of a mixed culture containing Escherichia coli, a culture obtained from untreated river water, and a culture obtained from sewage treatment plant activated sludge, said alkylaryl sulfonic acids having branched alkyl groups in which the total number of carbon atoms varies within the range of 6 to 18, said alkyl groups being derived from the product of condensation of low polymers of propene selected from the group consisting of dimer and trimer, thereby converting less than about 10 percent of said salts of alkylarylsulfonic acids to oxidized substances and forming a product mixture, and

(b) recovering water-soluble salts of alkylarylsulfonic acids from the product mixture of step (a).

5. A method according to claim 4 in which step (a) is operated as a semi-continuous multiple stage aerobic fermentation.

6. A method according to claim 5 in which less than 5 percent of the salts of alkylarylsulfonic acids are converted to oxidized substances in step (a).

7. A method according to claim 6 in which the watersoluble salts of alkylarylsulfonic acids are recovered in step (b) in the form of a dry powder.

References Cited in the file of this patent UNITED STATES PATENTS 1,494,435 Lipman May 20, 1924 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3, 138,543 June 23 1964 Raymond Co Allred et alo It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 4L2 for "develope" read develop column 3 line 26, for "hydrogen", second occurrence read aw hydrocarbon column 7, line 26 for "microbioligical" read microbiological column 8, line 8 for "semicontinnuous" read semi-continuous Signed and sealed this 24th day of November 1964,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD OF MANUFACTURE OF A MIXTURE OF WATERSOLUBLE SALTS OF SULFONIC ACIDS OF THE TYPE 